Figure 1.

Graphical illustration of a neutral model of genome evolution. A population of N = 4 organisms is shown, with genomes consisting of M = 3 genes. Colors denote different gene identities. We chose small values for N and M for illustrative purposes; realistic values are, e.g., N ~ 108 and M ~ 2000. (A) In a birth-death event an organism dies and is replaced by offspring of
another organism. The offspring genome is identical to the parent genome. (B) In a
gene transfer event a gene of one of the organisms is replaced by a gene from the
environment. We assume that this new gene has not been present in the population before